As awareness to protect the environment has been raised, control for an amount of exhaust gas of an automobile or the like has been strengthened. Accordingly, a variety of researches to enhance performance of an exhaust gas purifying catalyst that purifies exhaust gas discharged from an engine of the automobile have been performed.
The exhaust gas purifying catalyst usually has a configuration in which microparticles of noble metal such as platinum (Pt), palladium (Pd) and rhodium (Rh) are supported on a surface of a particulate metal oxide support made of alumina (Al2O3) or the like. By a catalytic function of such noble metal particles, the exhaust gas purifying catalyst converts harmful gas, such as unburned hydrocarbon (HC), carbon monoxide (CO) and nitrogen oxide (NOx), which is contained in the exhaust gas, into harmless water and gas.
Among the noble metals for use in the exhaust gas purifying catalyst, Rh is noble metal contained in the exhaust gas purifying catalyst since it is excellent in purification performance at a low temperature. With regard to the exhaust gas purifying catalyst containing Rh concerned, there is one using a Ce oxide as a compound that supports Rh (for example, Patent Document 1). This Ce oxide has an oxygen storage/release capacity, and accordingly, by being located in the vicinities of the noble metal particles, has a function as a promoter, specifically, has a function to suppress variations of the purification performance owing to variations of an atmosphere of the exhaust gas. Therefore, in the exhaust gas purifying catalyst using the Ce oxide as the compound that supports rhodium, an oxygen storage/release effect of the Ce oxide is exerted, the variations of the atmosphere in the peripheries of the noble metal particles are absorbed, and activity of the catalyst is enhanced, and eventually, the performance of the exhaust gas purifying catalyst can be enhanced.
Patent Document 1: Japanese Patent Laid-Open Publication No. 2004-298813